• Because many of the martian yardangs seem to be structurally controlled, structural influence must be carefully evaluated if yardang orientations are used to interpret wind directions on Mars. - Geological Survey professional paper, 1978

• There is little real diagnostic evidence on the yardang slopes themselves that they are wind eroded, since between the more intense winds that perform most of the removal there are probably periods in which rainfall or dew destroys the evidence. - Geomorphology in deserts, Ronald U. Cooke, Andrew Warren

Wikipedia:

A yardang is a streamlined hill carved from bedrock or any consolidated or semiconsolidated material by the dual action of wind abrasion, dust and sand, and deflation. Yardangs are elongate features typically three or more times longer than they are wide, and when viewed from above, resemble the hull of a boat. Facing the wind is a steep, blunt face that gradually gets lower and narrower toward the lee end. Yardangs are formed by wind erosion, typically of an originally flat surface formed from areas of harder and softer material. The soft material is eroded and removed by the wind, and the harder material remains. The resulting patter of yardangs is therefore a combination of the original rock distribution, and the fluid mechanics of the air flow and resulting pattern of erosion.